The study raises questions about the safety of standard training classes and whether or not soldiers had deployed to combat without realizing they suffered a mild traumatic brain injury.

The results are preliminary and rely on data gathered from hand-to-hand combat classes taken by nearly 2,000 soldiers at the Texas base. The post is one of the Army's main centers for basic training where soldiers spend more than 20 hours learning fighting techniques that include boxing, wrestling and Brazilian Jiu-Jitsu, according to the report.

Experts told ProPublica and NPR that they were concerned that brain injuries suffered prior to combat could have made soldiers more vulnerable to the long-term consequences of additional concussions, including frequent headaches and memory loss.

“Even 1 percent of soldiers would concern me,” Col. Carl Castro, the director of the Military Operational Medicine Research Program, told ProPublica and NPR. “I’d say we need to do something. We don’t want soldiers getting injured while training, if we can prevent it.”

There have been at least 244,000 traumatic brain injuries as a result of explosions and accidents since 2000, but previous reports from ProPublica and NPR found that number may be much higher due to underreporting and missed diagnoses.

Reporters who were permitted to observe advanced students learn how to teach combat-training classes in Fort Benning in Georgia witnessed one student get kicked in the head during a sparring match. That student appeared dazed, was evaluated by a medic and did not participate in the remainder of the class. He was later sent to a clinic for evaluation.

The ProPublica/NPR report said that hundreds of thousands of soldiers had taken the combat courses at bases nationwide in the past decade before deploying.